Commentary on the Effect of Electricity on Muscular Motion

...spinal marrow original: "medullæ"; completing the word from the previous page's catchword so that it touches a silver plate, and the other leg is allowed to slide freely on that same plate Fig. 11. Tab. 3., the muscles contract the moment the leg touches the surface. This causes the leg to lift and rise; soon after, however, it relaxes naturally and falls back onto the plate. As soon as it makes contact again, it is thrown upward once more for the same reason. This cycle of rising and falling continues, so that the leg seems to mimic an electric pendulum A device used in early physics to demonstrate electrostatic attraction and repulsion; here, Galvani sees the frog's leg acting as a self-triggering switch, much to the wonder and delight of the observer.

This phenomenon clearly demonstrates how effectively the plate acts as a substitute for a conducting arc arcus: a curved metal conductor used to bridge the gap between nerve and muscle to complete a circuit suited for this circuit. When the free leg lands on the plate, the circuit is completed; however, the circuit is broken as soon as the leg lifts away. The evidence that the metallic plate functions as a conducting arc is neither doubtful nor obscure.

It is difficult to describe the incredible power and suitability of this plate for exciting muscular contractions. The contractions are strong, frequent, and sometimes even sustained for a duration. This occurs not only if the hook fixed in the spinal marrow is pressed against the metallic plate or rubbed over it, but even at the very moment the hook touches the plate. Furthermore, once contact is made, even the slightest change in the contact between the hook and the plate—such as a light tap on the plate or the table the animal rests on—will trigger the effect. But enough has been said regarding the metallic plate acting as a type of conducting arc.

Before moving on from the use and power of the arc, I must mention something that demonstrates its effectiveness—and nearly its necessity—in these muscular contractions. They can be obtained, often even more clearly and promptly, not just with one arc, but with two arcs arranged so that the end of one arc is applied to the muscles and the end of the second arc to the nerves. When the two remaining ends are brought into contact with each other, or rubbed together if necessary Fig. 12, the contraction occurs. In this case, it is particularly notable that the electricity inducing these contractions does not seem to dissipate or spread through the hands holding the arcs, nor through the repeated contact of the arcs with the animal's body parts.